Share 'Function component can not handle "√" character? why?'

I want to insert a one variable function component, that looks like this:(√6/3)*xBut when I try to do this I get an error message: Syntax error: Invalid expression: Unexpected symbol encountered (√) Why I can not use squre root inside of a function? In this case I can easily write the √6 as a constant 2.449489742783178 But what if sometimes I need a variable under the square root: √x?   Thanks.